The invention relates to a communications method and apparatus for carrying communications traffic between devices, and in particular for carrying multimedia communications traffic between user devices. The invention is particularly, though not exclusively, applicable to virtual-circuit switched systems, such as asynchronous transfer mode (ATM) networks.
Telephony systems have evolved from simplistic hard-wired interconnected networks to broadband, high capacity systems that support multimedia, multi-mode communication devices on local area networks (LIANs) and packet-switched communication systems. Indeed, instead of having to rely entirely on dedicated land-line infrastructure, present day technologies now occupy virtual-channel environments in both the radio frequency and land-line domains.
The designers of today's narrowband communication systems, which typically employ pulse code modulation at a data rate of 64 kilo-bits per second (kbps), are presently considering the adaptation and development of these narrowband communication systems to support a migration to a multimedia environment having data rates of 2 Mega-bits per second (Mbps) or more. As will be understood, the requirement for migration arises as a direct consequence for the vast costs involved in deploying global communication systems, with ATM being touted as providing a low cost and simple package that is capable of supporting migration from narrowband (or wide-band) to broadband applications (principally in the intervening period before the full deployment of a free-standing Universal Mobile Telecommunication System (UMTS), for example).
It has also been necessary for designers to consider and anticipate the extensive and elaborate requirements for future control signalling and call management techniques. In this respect, new signalling schemes, such as AAL-2 negotiation procedures, have been developed to provide robust, high bandwidth communications at high data rates, while designers have also been keen to define system architectures in terms of “stacks” that comprise discrete layers of infrastructure or signalling protocols that each add functionality, capacity or control over a preceding layer in the stack.
The problems faced by system designers are further exacerbated by the fact that, to date, the various different forms of communication system, e.g. ATM, LANs and cellular radiotelephone schemes, operate distinct signalling and transport protocols that are incompatible on a network-to-network basis.
It is therefore clearly desirable to design and produce a communications systems architecture that supports varying types of present-day communications devices, and has the capability to interconnect different types of device which may use different signalling and transport protocols and to interconnect narrowband, wideband and broadband networks and other devices.